Photonic switches are used in order to redirect and transmit optical traffic signals between nodes of an optical network. At the heart of a photonic switching network lies a photonic switch fabric, which provides switching of optical traffic signals without the need for conversion of the signals to electrical form. Therefore, it is important to know when the switch fabric is no longer working properly since it will affect the workings of the network. As such, it is important to frequently verify the integrity of the connection paths within the switch fabric in order to ensure that the switch fabric is switching the optical traffic signals according to a desired mapping, and to further ensure that the power loss of the signals passing through the connection paths does not exceed an acceptable level.
A common method of testing switch fabrics is to inject an extraneous optical test signal into a particular connection path of the switch fabric and take measurements of that extraneous optical test signal both before and after it has been injected into the switch fabric. By comparing the level of similarity of the measurements taken before and after the extraneous optical test signal has traveled through the particular connection path, the validity and power loss of the particular connection path can be determined.
However, a deficiency with the aforementioned method of verifying switch fabric connection paths is that the verification process can only take place while the connection path is not being used as an active connection path. Therefore, in order to test a selected connection path, the extraneous optical test signal must be injected within a connection path that is not being used to transmit an optical traffic signal. As such, a switch fabric connection path cannot both be tested and convey an optical traffic signal at the same time.
A further deficiency with the aforementioned method of switch fabric verification is that additional hardware components must be provided in order to generate the extraneous optical test signal. These additional components include, at a minimum, a source of extraneous light, which takes up space. Moreover, these additional components add to the cost of the photonic switch.
It can be seen that there is a need in the industry for an improved technique for performing switch fabric verification.